Thermal coupling of a high temperature PEM fuel cell with a complex hydride tank

Sodium alanate doped with cerium catalyst has been proven to have fast kinetics for hydrogen ab- and de-sorption as well as a high gravimetric storage density around 5 wt%. The kinetics of hydrogen sorption can be improved by preparing the alanate as nanocrystalline material. However, the second decomposition step, i.e. the decomposition of the hexahydride to sodium hydride and aluminium which refers to 1.8 wt% hydrogen is supposed to happen above 110 degrees C.

The discharge of the material is thus limited by the level of heat supplied to the hydride storage tank. Therefore, we evaluated the possibilities of a thermal coupling of a high temperature PEM fuel cell operating at 160-200 degrees C. The starting temperatures and temperature hold-times before starting fuel cell operation, the heat transfer characteristics of the hydride storage tanks, system temperature, fuel cell electrical power (including efficiency) as well as alanate kinetics were varied by system modelling with gPROMS (R).

The kinetics of the hydride decomposition was found to have a major influence on the performance of the system. A cumulative output of 0.8 kWh was reached in a test run.